In a conventional electrophotographic image forming apparatus, after a toner image is transferred onto a transfer paper sheet or an intermediate transfer member, unnecessary transfer residual toner adhering to the surface of an image bearer as the cleaning target member, such as a photoconductor, is removed with a cleaning blade serving as a cleaning unit. A strip-shaped blade member is used as this cleaning blade, because such a blade member generally has a simple structure and shows excellent cleaning performance.
In a cleaning blade of a blade cleaning system, the blade member is supported by a supporting member that is made of a material having high rigidity such as a metal and is fixed to the main frame of a cleaning device, and the edge line portion of the blade member is pressed against the peripheral surface of an image bearer, to remove adhering matter adhering to the image bearer. Such a cleaning blade of a blade cleaning system has a simple structure, is inexpensive, and excels in adhering matter removal performance. Accordingly, such cleaning blades are widely used.
Patent Document 1 discloses a cleaning blade that includes a blade member having a double-layer stack structure formed with elastic members having different characteristics from each other. The edge line portion of the edge layer to be brought into contact with an image bearer as the cleaning target member is impregnated with a resin, and the surface of the impregnated edge line portion is further coated with a surface layer having a relatively high degree of hardness, so that the hardness of the edge line portion is increased.
In the cleaning blade disclosed in Patent Document 1, the hardness of the edge line portion is increased with the impregnated portion and the surface layer. Accordingly, deformation at the edge line portion becomes smaller, and an increase in the contact area can be prevented. Thus, the contact pressure can be set at a high value, and cleaning performance can be improved.
The inventors observed the contact pressure that was applied to an image bearer by a blade member over a long period of time. As a result, the inventors discovered that the blade member was permanently deformed into a curved shape, or permanent deformation occurred. The contact state varied from the initial contact state, the contact pressure became lower, and there was a possibility of defective cleaning. Even in a case where a blade member having a double-layer stack structure formed with an edge layer having a high degree of hardness and a backup layer having a low degree of hardness was used, the edge line portion was subjected to an impregnation treatment, and the impregnated portion was further coated with a surface layer, the initial excellent cleaning performance was not fully maintained depending on a combination of permanent elongation rates of the edge layer, the backup layer, and the edge line portion.